Formula and example
How it is calculated
F = L/(4πd²)
Worked example
100 W emitted isotropically spreads over approximately 1,256.64 m² at a distance of 10 m, giving approximately 0.07958 W/m².
Things to check
- Doubling the distance spreads the same power over four times the area.
- Absorption, shielding, directional emission and cosmological effects are excluded.